1. Field of Invention
The present inventions relate in general to ultraviolet ray lamps and to sterilizers and cleaners using ultraviolet light. More specifically, the inventions described herein feature ultraviolet ray lamps having a predetermined spectrum of wavelengths.
2. General Background and Related Art
Various devices and apparatus, such as sterilizes, utilize ultraviolet ray lamps. Generally, an apparatus for treating fluid, such as a sterilizer, or an air cleaner utilizes an ultraviolet ray lamp. It is desired that such apparatus effectively remove or decompose harmful ingredients. Usually, an apparatus for treating water includes a water tank for collecting water including harmful ingredients. An ultraviolet ray lamp is arranged in proximity to the water and irradiates ultraviolet rays into the water in order to remove or decompose harmful contaminants.
An ultraviolet ray lamp of this type comprises an ultraviolet rays-transmitting glass bulb made of soft glass, or quartz glass. The transmittance of quartz glass is higher than that of soft glass, so quartz glass is usually used for the glass bulb.
An ultraviolet ray lamp having quartz glass bulb can irradiate ultraviolet rays having wavelengths of 254 nm and 185 nm. Ultraviolet rays of 185 nm decompose molecular oxygen (O2) of air into atomic oxygen (O). Then, atomic oxygen (O) bonds with molecular oxygen (O2), to form ozone. Ozone is a sterilizer, however it is harmful to our health at a strong concentration. The concentration of ozone is preferably maintained at 0.1 ppm or less to minimize health risk. For example, in case of a sterilizer or an air cleaner using an ultraviolet ray lamp, if the apparatus is set up indoors, ozone generated causes a bad smell. It is also harmful to health to have too strong a concentration of ozone.
Japanese Laid Open Patent Application HEI 10-69886 discloses an arrangement for minimizing the production of ozone. It includes a quartz glass bulb (hereafter referred to as ‘ozone-less quartz glass’) containing titanium oxide (TiO2), or cerium oxide (CeO2) and a zirconium oxide (ZrO2) film formed on the inner surface of the quartz glass bulb. The ozone-less quartz glass can transmit ultraviolet rays of 254 nm that are generated by mercury (Hg), but do not easily transmit ultraviolet rays of 185 nm that are generated by mercury (Hg). The ozone-less quartz glass has a characteristic of absorbing ultraviolet rays of 220 nm or less because, for example, titanium oxide (TiO2) contained in the quartz glass bulb, absorbs ultraviolet rays of the comparatively short wavelength. However, if titanium oxide (TiO2) is excessively contained in the quartz glass, titanium oxide (TiO2) starts to absorb ultraviolet rays of the comparatively long wavelength. Therefore, the quantity of the titanium oxide (TiO2) is exactly controlled to ten PPM or less. In the case of utilizing ozone-less glass, ultraviolet rays of 185 nm are absorbed at the inner surface of the glass bulb, so that its ultraviolet rays do not reach the outer surface of the glass bulb.
In general, it is known that ozone-less quartz glass tends to shrink when it is bombarded with ultraviolet rays of 185 nm. When using ozone-less quartz glass, the glass bulb shrinks at its inner surface, but does not shrink at its outer surface. Therefore, a strain occurs on the surface of the glass bulb. If there is a flaw on the outer surface of the bulb when it is manufactured, the bulb may crack due to the strain when it is operated. Because the zirconium oxide (ZrO2) film absorbs ultraviolet rays of 185 nm, the ozone-less quartz glass bulb does not strain easily and is less likely to crack.
However, the above-described ultraviolet ray lamp cuts off most of the ultraviolet rays of 185 nm. Thus, the ultraviolet ray lamp, which does not easily crack, is not very efficient at producing ozone generated by ultraviolet rays of 185 nm in order to sterilize.